SOFIA, Bulgaria (AP) — The defector from communist Bulgaria was jabbed in the thigh with a poisoned umbrella tip in one of the most sensational assassinations of the Cold War.

Thirty-five years later, no one has been convicted of Georgi Markov’s murder. Further dimming hopes the killing will ever be officially solved, Bulgaria’s chief prosecutor on Thursday announced his office has closed its probe, saying the statute of limitations had been reached and it was leaving the case to British authorities.

The decision drew outrage from critics who say post-communist authorities have dragged their feet on evidence the KGB and Bulgarian secret police were involved.

In September 1978, Markov was waiting at a London bus stop when he was jabbed. The journalist and harsh critic of his country’s communist regime in reports for the BBC and Radio Free Europe died four days later.

British government scientists discovered the umbrella had been used to inject a pinhead-sized pellet of the poison ricin into Markov’s leg. The fatal pellet is one of the artifacts in a macabre crime museum — closed to the public — inside Scotland Yard headquarters, alongside letters from Jack the Ripper and other grim mementoes.

Prosecutor Sotir Tsatsarov said his office was ready to provide legal assistance to British authorities. Unlike Bulgarian law, there is no statute of limitations on murder in the U.K.

Bulgaria was the most loyal Soviet ally under decades of communist rule. Post-communist leaders had vowed to clear the Markov case in an effort to clean up Bulgaria’s image, but as with trials of former communist leaders, police officers and labor camp guards, they have failed to make much progress and the results have been spotty.

In closing the case, “Bulgaria and its prosecution are admitting to being either powerless or lacking the will to reveal one of the most horrific crimes of the communist regime — murder over speech, not action,” prominent columnist Petya Vladimirova wrote on Thursday.

Suspicions that Bulgarians were involved in the killing grew after Oleg Kalugin, a former KGB agent, said in 1992 that Bulgaria asked Moscow for help in the assassination.

The next year, Danish authorities charged a Dane of Italian origin, Francesco Guillino, with killing Markov. Guillino, who reportedly had worked for the Bulgarian secret services since 1972, denied wrongdoing and eventually was freed while Danish police awaited further evidence from Bulgaria that never came. He left Denmark and was believed to have settled in Hungary or Romania.

A Bulgarian journalist claimed in 2005 that he had found evidence confirming the slaying was plotted and carried out by Bulgaria’s former communist secret services and that Bulgaria’s post-communist authorities had covered up the case.

In Hristo Hristov’s book, titled “Kill Vagabond,” a reference to Markov’s code name with Bulgaria’s secret service, the author also points to Guillino as the probable assassin and argues that his involvement was covered up by the National Intelligence Service, the Bulgarian successor to the communist service.

London’s Metropolitan Police said its investigation remains open. The force said the case is “a particularly complex investigation, and we continue to work with the appropriate international authorities to investigate any new information that is passed or made available to police.”

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Associated Press Writer Jill Lawless contributed to this story from London.